The invention relates to a blade for a fluid flow engine, particularly to the blades of a gas turbine. The invention also relates to a method for manufacturing such blades.
Gas turbine blades with a protective coating are known in the art. Such prior art blades are made of metal and the protective coating comprises primarily a diffusion layer made, for example of aluminum, chromium or platinum. Prior art protective coatings may be applied as a sprayed layer, for example made of cobalt, chromium, aluminum, yttrium or zirconium oxide (ZrO.sub.2). These prior art protective layers serve as corrosion protection layers. Where zirconium oxide is used as the protection layer, the layer operates as a thermal insulation or thermal barrier. It is also known to apply organic or inorganic varnish or sprayed layers especially of tungsten carbide (WC) onto the surface of metal turbine blades to provide an erosion protection. It is further known to provide turbine blades with enamel coatings for damping blade vibrations.
The protective coatings of the prior art are primarily intended for a specific purpose such as heat insulation, corrosion prevention, or vibration damping. However, especially in connection with many gas turbines combined or simultaneous requirements must be satisfied by the protective coatings, for example, to counter the simultaneously occurring large erosion and corrosion effects on the blades. These combined load effects causing wear and tear in many gas turbines are very large where the fuel is an alternative fuel such as furnace gas, as compared to oil. The wear and tear effects are extremely large in gas turbines which are operated with a gas produced as an alternative fuel by the combustion of coal dust. Such coal dust fuel is loaded with solid particles which are entrained in the fuel flow and are therefore erosive as well as corrosive.
Currently, gas turbine blades are being tested which are made of ceramic materials. Such ceramic material turbine blades have been found to have good corrosion and erosion resistance as compared to gas turbine blades made of metal provided that the fuel gas is moderately corrosive. A material removal from the blades of ceramic material cannot be prevented, however.